Vibration devices of this type are generally designed in such a way that one of the eccentrics is fixed and the other is capable of movement relative to the rotating shaft. The vibration amplitude is reset by changing the direction of rotation of the shaft. The disadvantage of these known amplitude-changing devices is that breakdowns frequently occur in the rotating shaft and its bearings, as well as in the hydraulic drive system, because of the vibration arising if the change from high to low amplitude and vice versa is carried out too rapidly.
In the case of instantaneous amplitude changes, all the kinetic energy of the rotating shaft is absorbed in an extremely short time. As mentioned above, this gives rise to high mechanical stresses in the rotating shaft and also sudden pressure surges in the hydraulic system. Instantaneous amplitude changes also give rise to heavy impacts when the movable eccentric strikes the fixed eccentric mounted rigidly on the eccentric shaft. Attempts have been made to avoid this by covering the contact surfaces of the respective eccentrics with shock-absorbing material such as rubber pads. However, such rubber pads disintegrate rapidly and have a comparatively short service life.